Prosthetic devices that are delivered intraluminally, such as stents, valves, occluders, shunts, etc., are typically designed to be self-expanding or balloon-expandable such that they engage the walls of the vessel or duct at the treatment site. To ensure that the prosthesis does not migrate after placement, anchoring barbs configured to embed into adjacent tissue may be employed to hold the device in place. Barbs are an especially important component of endovascular stent grafts, which are used to exclude an aneurysm sac formed in a blood vessel. The high velocity of blood within the aorta makes it essential to securely anchor the prosthesis when treating an aortic abdominal aneurysm (AAA). Migration of the device downstream can result in the proximal seal of the aneursym sac being compromised, which could be catastrophic in the event that the aneurysm sac ruptures. Barb fixation is thus employed in a variety of intraluminal prostheses, such as the ZENITH® Endovascular Stent Graft (Cook Incorporated), which relies on barbs to anchor the proximal end of the device in the healthy portion of the aorta above the renal arteries.
In an intraluminal prosthesis formed from a wire frame or support structure, the barbs typically comprise separate elements attached to the frame at strategic points therealong. Typically, short sections of material are soldered to struts of the frame such that they extend outward for engaging tissue. In the body, solder is subject to corrosion when in contact with bodily fluids, and therefore mechanical methods of attachment have been used as an additional measure to reduce the incidence of barb failure. However, in environments in which there are repetitive mechanical stresses, barb failure due to fracture of the strut or weld remains a relatively common phenomenon. Such failures may be attributed in part to limitations of the barb design and the method of manufacture and/or attachment.
Laser welding is another technique commonly employed for attaching barbs to struts of an intraluminal prosthesis. Due to the localized heating of this process, however, a heat-affected zone having a nonuniform microstructure may be formed at the site of the weld. The heat-affected zone may include coarse grains, undesirable precipitates, and/or increased levels of impurities that can cause embrittlement of the microstructure, thereby increasing the likelihood of barb failure.
Accordingly, an improved attachment method that can reliably bond a barb to a strut of an intraluminal prosthesis is desired.